The overall goals of the present application for erythropoietin (Epo) studies are: 1) to develop and refine assay methods which can be of use in 1) assessing purification techniques, in enhancing chemical studies and in investigating erythroid kinetics; 2) to develop methods based on in vitro production of erythropoietin as a possible mechanism for acquistion of hormone suitable for therapeutic use and to identify cellular sites of production of Epo; 3) to continue our studies which could lead to a better understanding of the control of erythropoiesis in pregnancies, chronic uremia and cyclic hematopoiesis. Specifically, the assay methods which will be investigated include a new avenue of approach by the use or radio-receptor assays utilizing Epo responsive fetal liver cells, and the following immunological techniques: 1) immunoradiometric assay in which purified anti-Epo antibodies are radiolabeled, 2) conventional radioimmunoassay, and 3) agglutination techniques by which sensitization of synthetic beads in place of red blood cells and the attachment of antibody to solid surface walls. These assay techniques will be compared to our already developed bioassay and immunological techniques. Studies will be expanded in determining the cellular sites of production of Epo and identifying Epo responsive cells by electron microscopic technique. The factors necessary for production of erythropoiesis stimulating factors by cells in tissue culture will be carried out. Our final aim is to assess the role of erythropoiesis control mechanisms in pregnancy, chronic uremia as well as human and canine cyclic hematopoiesis.